On a daily basis, vast quantities of water are removed from rivers, lakes, and streams for potable water use and for use in a variety of industrial processes. The greatest industrial use of water is for cooling purposes, and the greatest non-consumptive industrial demand for water as a heat transfer medium comes from the steam-electric generating industry. Also, municipalities draw water for public consumption.
In water conduits, such as those used for industrial and commercial use, it is necessary to be able to conduct relatively large amounts of water to the desired industrial or municipal end use.
Source water supports an abundance of biological life forms, many of which cannot be removed from water before it is used. While some of these biological life forms may not adversely effect municipal or industrial treatment processes, zebra mussels are a biofouling organism which have become a severe problem in North America in a very short time. These mussels foul piping and equipment surfaces in municipal water treatment plants and industrial water systems.
Growths of sessile organisms such as mussels are of frequent occurrence on the walls of water pipes. Their presence is unwelcome mainly for two reasons: first because by reducing the effective bore of the pipe and increasing the roughness factor, they diminish the water carrying capacity of the system, and second, through setting up local differences in the state of oxidation on the inner surface they can be responsible for electro-corrosion of steel and cast-iron pipes. These consequences are responsible for much waste in the water supply industry in increased pumping costs, loss of water carrying and treatment capacity, in pipe cleaning, maintenance and replacement. Similarly, in the electrical power generation, the chemical, refinery and other industries they are responsible for diminished cooling capacity, lower production capacity and the more frequent cleaning maintenance and replacement.
The zebra mussel attaches itself to objects such as water pipes by up to 200 tough fibers of a dry horny material (the byssus) and usually leads a sessile existence. Frequently, the mussels fix these lyssel threads to other mussels, thus forming clusters in open water, and layers of up to a foot or more on walls and pipes.
The zebra mussel was unknown in the Laurentian Great Lakes prior to 1988 when substantial infestations were discovered in southeastern Lake St. Clair. Presumably, the mussels were introduced with ballast water discharged from the tanks of international shipping bout two years earlier. They have spread throughout Lake Erie with phenomenal speed and reports of their presence at Green Bay, Wis. and Gary, Ind. on Lake Michigan imply that it is only a matter of time before all the Great Lakes and the adjacent Mississippi and Ohio River Basis are affected. With time, the threat may extend to every body of surface water in North America.
The explosive development of the mussel population in western Lake Erie has prompted dire predictions for the future. The number of animals per unit area promises to increase exponentially, especially during the years immediately following the initial infestation.
A wide variety of methods have been used in an attempt to control the growth of zebra mussels.
Various methods have been proposed for the removal of existing growth of the zebra mussel such as by scraping the mussels from mains and tanks. This method is not only slow and expensive but the greatest drawback is that it cannot be expected to remove every mussel from the pipe mains and cooling or heat exchange equipment. Moreover, it means that the pipe mains and other equipment cannot be in service during the treatment intended to remove the Zebra Mussel.
High pressure water has also been used for removing zebra mussels from walls, trash racks, or other equipment. A suction pump is normally attached to a mechanical scrapper which can be used to dislodge and vacuum the zebra mussels out of an area. This method of course has the disadvantage of requiring operation and maintenance of the equipment by a work force; and may not be applicable to all water conduits, such as those of smaller diameter. An example of such mechanical cleaning apparatus is that taught in U.S. Pat. No. 5,069,722.
Another method which has been used for controlling Zebra Mussels is the application of toxic and non-toxic coated materials which can either prevent zebra mussel settlement or cause very weak byssal attachment (so that the mussels can be more easily removed). These products include silicone and epoxy compounds, copper-based paints, and thermal metallic sprays. These materials can be used on structures that are difficult to clean or if there are anticipated difficulties with removal and disposal of large numbers of zebra mussels. Some of the drawbacks of the use of such coatings include the expense of the coatings and their application, and the possibility that some coatings may be inappropriate for some applications due to the end use of the water; e.g. in municipalities and for certain chemical or other industrial operations.
Many oxidizing and non-oxidizing chemical control agents have also been used to reduce or eliminate zebra mussels. Chlorine is a commonly used control agent in Europe, this country, and Canada. Continuous exposure to chlorine at 0.5 mg/L will kill zebra mussels in 14-21 days, which is preferable to application of a concentrated "slug dose" that zebra mussels can withstand for several days by closing their shells. Chlorine can be used in pipes or ducks that contains pressure sensing or other equipment. Chlorine has bee proposed for the removal of the mussels and dosing of the water with up to 50 ppm chlorine as it flows through the main for periods upwards of two weeks has been shown to be a reliable method of control.
However, the use of chlorine for such purposes has certain obvious disadvantages since it is quite toxic to humans and animals and is corrosive to the operating equipment. It produces undesirable often toxic, even carcinogenic, chlorinated organic compounds in the water.
A wide variety of other chemical agents have been used in attempt to control zebra mussel growth. These include the use of a nitrostyrene compound and an alkyl thiocyanate compound as taught in U.S. Pat. No. 4,579,665; the use of a water-soluble alkyl guanidine salt as taught in U.S. Pat. No. 4,816,163; the use of a water-soluble quaternary ammonium salt, such as those taught in U.S. Pat. No. 4,857,209; the use of an alkylthioalkylamine or acid addition salt thereof, such as that taught in U.S. Pat. No. 4,970,239; the use of a water-soluble dialkyl diallyl quaternary ammonium polymer (polyquat), such as that taught in U.S. Pat. No. 5,015,395; the use of an effective amount of ozone, such as that taught in U.S. Pat. No. 5,040,487; the use of didecyl dimethyl ammonium halide such as taught in U.S. Pat. No. 5,062,967; the use of a combination of a chlorine solution and a bromide salt capable of releasing bromide ions, such as taught in U.S. Pat. No. 5,141,754; and the use of glutaraldehyde, such as taught in U.S. Pat. No. 5,160,047.
Chemical methods such as those described above have the obvious disadvantages of requiring the purchase of expensive chemicals as well as, in many cases, the need to use skilled operators in their application. Chief among the disadvantages of such chemical methods is of course the toxic and polluting effect that these chemicals can have for the end user, such as municipalities, or for the environment at large.
Still another disadvantage of many of the above-described methods is that such methods cannot be effectively used while the water is flowing through the conduit. Flowing water may have the effect of diluting the chemical agents below their respective effective concentration.
Accordingly, it is desirable to be able to develop a method for controlling zebra mussels which may be applied to a flow of water, particularly those used for the necessary throughput in municipal and industrial applications.
It is yet another object of the present invention is to provide an efficient flow of water which has been treated to control macrofouling pests, such as zebra mussels.
It is also desirable to be able to develop such a method which can be applied without the need to use skilled operators or workmen in the process.
In view of the present disclosure and the practice of the present invention, other advantages or the alleviation of other problems may become apparent.